Use the File Manager to edit /app/data/settings.yml.

See this file for the possible options.

When performing changes, it's recommended to do only one change at a time.
Click: Save + Close
Then click to Restart the App (to apply the changes)

If some change has resulted in SearXNG to not be back online in 5+ minutes, just revert back the change and Restart SearXNG.
Then it will be back online.